Minimally invasive direct coronary artery bypass (MIDCAB) surgery, both via sternotomy and alternative incisions, is a substantially revolutionary development in surgery for allowing bypass surgery to be conducted on a beating heart. However, beating heart surgery shows an undesirably higher rate of early graft failure than conventional coronary artery bypass procedures using cardiopulmonary bypass and cardioplegia. The technical difficulty of sewing the coronary artery anastomosis on a beating heart is likely an important factor in this difference in outcome between the two techniques. Controlled intermittent asystole (CIA) during brief intervals required for placing anastomotic sutures is suitable for improving the precision of coronary anastomoses performed on a beating heart and reducing graft failure while increasing ease of operation.
Cardiopulmonary bypass (CPB) and chemical arrest using cardioplegia solutions have traditionally provided surgeons with optimal operative conditions: hemodynamic control and cardiac quiescence. This optimal field has contributed to technical success in increasingly complex cardiac surgical operations. However, there has been recent interest in performing coronary artery bypass surgery without either complete cardiopulmonary bypass or cardioplegia. The quality of the distal anastomosis is a primary concern among cardiac surgeons who observe and perform coronary artery bypass graft (CABG) procedures unaided by cardioplegic arrest and cardiopulmonary bypass. Coronary artery bypass graft failure rates reported with minimally invasive direct coronary artery bypass range from 3.8 to 8.9%, while traditional CABG on CPB has a reported anastomotic failure rate of 0.12%. This may reflect a difference in anastomotic precision between MIDCAB and CPB-aided CABG. Although the benefits of avoiding extracorporeal circulation and global cardioplegia in beating heart procedures are important, they do not outweigh the performance of an optimal coronary anastomosis.
The key difference in the anastomotic results between conventional CABG and beating heart CABG is related to achieving elective asystole during construction of the distal anastomosis. Cardiac motion can be minimized during MIDCAB procedures via pharmacologic bradycardia (adenosine, .beta. blockade) and mechanical stabilization using various devices. Although these techniques do improve operative conditions, they only approximate the advantages of elective asystole achieved with CPB and cardioplegia. Applicants show that a state of controlled intermittent asystole (CIA) is produced off CPB, which provides a major advantage otherwise gained by cardioplegic arrest on CPB. In particular, CIA is achieved using unilateral (or bilateral) vagus nerve stimulation coupled with pharmacologic suppression of electromechanical escape activity.
Applicants demonstrate that elective, controlled intermittent asystole is produced by vagus nerve stimulation after treatment with an acetylcholinesterase inhibitor, a .beta.-adrenergic receptor blocker, or a calcium channel blocker, or combinations thereof.